Hypo + Hypernatraemia Flashcards
What is hypernatremia?
High plasma Na+ conc
>146mmol/L
Causes of hypernatremia
- osmotic diuresis e.g. uncontrolled diabetes
- fluid loss without replacement e.g. sweating, burns, vomiting
- diabetes insipidus
- incorrect IV fluid replacement
- primary aldosteronism
Symptoms of hypernatraemia
- thirst
- apathy
- irritability
- weakness
- confusion
- reduced consciousness
- seizures
- hyperreflexia + spasticity
- coma
What is apathy?
a lack of motivation or lack of interest in things around you
Different types of hypernatremia + their causes
Hypovolaemic hypernatraemia
- osmotic diuresis
- loop diuretics
- intrinsic renal disease
- excessive sweating
- burns
- diarrhoea
.
- Euvolaemic hypernatraemia:
- diabetes insipidus
- hypodipsia
.
Hypervolaemic hypernatraemia:
- primary hyperaldosteronism
- Cushing’s syndrome
- hypertonic dialysis
- sodium chloride tablets
Treatment of hypernatraemia
- identify underlying cause + reverse if possible
- increase water intake
- IV fluids dextrose in water - no sodium
- monitor sodium levels
Symptoms of hyponatraemia
- headache
- N+V
- malaise
- confusion
- agitation
- drowsiness
- gait imbalance
Investigations of hyponatraemia
- plasma osmolality
- urine osmolality
- urine Na+
- TFTs
- cortisol levels
- CT head if suspected SIADH
- drug history
- hydration status
Diagnostic pathway of hyponatarmia
- exclude non-hypo-osmolar hyponatraemia (e.g. hyperglycaemia)
- then check urine osmolality
- urine osmolality <100mosmol/kg - primary polydipsia or inappropriate IV fluids
- urine osmolality >100mosol/kg - check urine Na
- urine Na >30mmol/L - GI loss, CCF, nephrotic syndrome, cirrhosis
- urine Na <30mmol/L - SIADH, vomiting, primary salt wasting, Addison’s disease
What does a urine sodium of >30mmol/l suggest?
Low effective arterial volume
due to true dehydration *e.g. GI salt loss
Or CCF, cirrhosis or nephrotic syndrome
What does urine sodium >30mmol/L suggest?
if euvolaemic - SIADH
if dehydrated - Addison’s disease, renal + cerebral salt wasting + history of vomiting
What causes hypovolaemic hyponatremia?
Renal losses:
- thiazide diuretics
- osmotic diuresis
- Addison’s disease
.
Non- renal losses:
- diarrhoea
- vomiting
- seating
- burns
- pancreatitis
Why does vomiting cause hyponatramia?
causes loss of H+ > metabolic alkalosis
corrected by renal excretion of sodium bicarbonate
What drugs can cause hyponatremia?
- thiazides
- SSRIs
- PPIs
- ACEi
- loop diuretics
Treatment of hypovolaemic hyponatraemia
- give IV fluids: 0.9% saline at 1-3ml/kg/hour
- give K+ if needed
What are the causes of euvolaemic hyponatraemia?
- primary polydipsia (excessive fluid consumption)
- adrenal insufficiency
- SIADH
- hypothyroidism
Diagnosis of SIADH
after exlusion of hypothyroidism, total salt depletion + ACTH deficiency
What is SIADH characterised by?
low serum osmolality
urine osmolaility >100mosol/kg
urine Na >30mmol/l
treatment of SIADH
- fluid restriction <800ml/day
- PO sodium chloride
- furosemide
- demeclocycline induces diabetes insipidus (opposite to SIADH)
What are causes of hypervolaemic hyponatraemia?
- congestive cardiac failulre
- nephrotic syndrome
- liver cirrhosis
Treatment of hypervolaemic hyponatraemia
fluid restrict
consider furosemide
What is the risk of correcting hyponatraemia too fast?
- too rapid correction of chronic hyponatraemia leads to central pontine myelinosis
- aim to correct <12mmol/L/day
Treatment of acute hyponatraemia
3% hypertonic saline IV bolus +/- furosemide
Treatment of chronic hyponatraemia
- hypertonic saline bolus if seizures present
- isotonic saline + furosemide if not
- aim to correct 8mmol/L in 24 hours
- fluid restriction if asymptomatic
- stop offending drugs
How do you calculate osmolarity?
Osmolarity = (2xNa) + glucose + urea
mmol/L
What is cerebral salt wasting syndrome?
Renal loss of Na+ during intracranial disease
- Causes hyponatremia + decrease in extracellular fluid volume
What can occur in rapid onset hyponatremia?
Pontine demyelination
What is hypo+hypernatremia nearly always a problem of?
Fluid imbalance
